Enhanced slag formation for copper-containing gas generants

ABSTRACT

Gas generants comprising copper are provided that have improved slagging ability. In certain aspects, the gas generants include a fuel, an oxidizer comprising basic copper nitrate, and a large particle size endothermic slag-forming component, such as aluminum hydroxide (Al(OH) 3 ). The gas generants may be cool burning, e.g., having a maximum flame temperature at combustion (T c )≦about 1,900K (1,627° C.). The disclosure also provides methods of enhancing slag formation for a gas generant composition that comprises copper. Such methods enhance slag formation during combustion of the gas generant composition by at least 50%.

FIELD

The present disclosure relates to enhancing slagging in gas generants containing copper by introducing large particle size endothermic slag-forming components.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

Passive inflatable restraint systems are used in a variety of applications, such as motor vehicles. Certain types of passive inflatable restraint systems minimize occupant injuries by using a pyrotechnic gas generant to inflate an airbag cushion (e.g., gas initiators and/or inflators) or to actuate a seatbelt tensioner (e.g., micro gas generators), for example. Automotive airbag inflator performance and safety requirements are continually increasing to enhance passenger safety, while concurrently striving to reduce manufacturing costs.

Thus, increasing functionality of a propellant or a gas generant used in airbag inflators, while improving performance and reducing costs of the entire airbag inflator system has been an ongoing objective in design of inflatable restraint systems. Gas generant selection involves addressing various factors, including meeting current industry performance specifications, guidelines and standards, generating safe gases or effluents, durational stability of the materials, and cost-effectiveness in manufacture, among other considerations. Improved gas generator performance may be achieved in a variety of ways, many of which ultimately depend on the gas generant formulation to provide the desired properties.

Suitable gas generants provide sufficient gas mass flow in a desired time interval to achieve a required work impulse for the inflating device. Further, gas generants having lower flame temperatures are advantageous. In current designs of automotive airbag inflators, a significant portion of the mass of the inflator is often relegated to heat sink, in combination with filtration systems. This detrimentally impacts the weight of the inflator and thus the efficiency of the system. Hence, for new advanced inflator designs, it is desirable to reduce or minimize filter and heat sink requirements as much as possible. As part of these new designs, cool burning gas generant formulations are advantageous because they reduce heat sink requirements. Additionally, if filter mass is to be reduced the cool burning gas generant must slag very well, meaning that combustion products form a large integral mass that is retained inside the combustion chamber during combustion and thus does not pass through the filter into the airbag. Accordingly, enhancing formation of slag in various gas generants, especially in cool burning gas generants would be highly desirable to produce lighter, more efficient inflator designs.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

The present disclosure pertains to gas generant compositions comprising copper having improved slagging properties. For example, in certain variations, the present disclosure provides a gas generant composition comprising a fuel, an oxidizer comprising basic copper nitrate, and an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm. The gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.).

In another variation, the present disclosure provides a gas generant composition comprising a fuel, at least one oxidizer comprising basic copper nitrate, and an endothermic slag-forming component comprising aluminum hydroxide having an average particle size diameter of greater than or equal to about 150 μm. The gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.). In certain aspects, such a gas generant composition may have a maximum flame temperature at combustion (T_(c)) of greater than or equal to about 1,350K (1,077° C.) to less than or equal to about 1,450K (1,177° C.).

In yet another variation, the present disclosure provides a method of enhancing slag formation for a gas generant composition. The method may comprise introducing an endothermic slag-forming component having an average particle diameter size of greater than or equal to about 150 μm to a gas generant composition comprising a fuel and an oxidizer comprising basic copper nitrate. The introducing of the endothermic slag-forming component enhances slag formation during combustion of the gas generant composition by at least 50%.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a partial cross-sectional view of an exemplary passenger-side airbag module including an inflator for an inflatable airbag restraint device.

FIG. 2 shows an acceptable particle size distribution for a large particle size endothermic slag-forming aluminum hydroxide for use in accordance with various aspects of the present disclosure.

FIG. 3 shows a macroscopic photograph of a slag formed from a conventional gas generant.

FIG. 4 shows a microscopic photograph of the slag in FIG. 3 formed from the comparative example of a conventional gas generant. Magnification is at 50 times.

FIG. 5 shows a macroscopic photograph of a slag formed from a gas generant prepared in accordance with certain aspects of the present disclosure.

FIG. 6 shows a microscopic photograph of the slag in FIG. 5 formed from the gas generant prepared in accordance with certain aspects of the present disclosure. Magnification is at 50 times.

FIG. 7 shows a photograph of a slag formed from a comparative conventional gas generant in a post-fire inflator combustion chamber.

FIG. 8 shows a photograph of slag formed from the gas generant prepared in accordance with certain aspects of the present disclosure in a post-fire inflator combustion chamber.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various components, elements, regions, layers and/or sections, these components, elements, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “primary,” “secondary,” “first,” “second,” or and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first or primary component, element, region, layer or section discussed below could be termed a secondary component, element, region, layer or section without departing from the teachings of the example embodiments.

Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters.

As referred to herein, ranges are, unless specified otherwise, inclusive of endpoints and include disclosure of all distinct values and further divided ranges within the entire range. Thus, for example, a range of “from A to B” or “from about A to about B” is inclusive of A and of B. Disclosure of values and ranges of values for specific parameters (such as weight percentages, temperatures, molecular weights, etc.) are not exclusive of other values and ranges of values useful herein. It is envisioned that two or more specific exemplified values for a given parameter may define endpoints for a range of values that may be claimed for the parameter. For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that Parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if Parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, and 3-9. Example embodiments will now be described more fully with reference to the accompanying drawings.

The present disclosure is drawn to gas generant compositions and methods for enhancing slag formation in such gas generant compositions. Gas generants, also known as propellants, gas-generating materials, and pyrotechnic materials are used in inflators of airbag modules, such as a simplified exemplary airbag module 30 comprising a passenger compartment inflator assembly 32 and a covered compartment 34 to store an airbag 36 of FIG. 1. A gas generant material 50 burns to produce the majority of gas products that are directed to the airbag 36 to provide inflation. Such devices often use a squib or initiator 40 which is electrically ignited when rapid deceleration and/or collision is sensed. The discharge from the squib 40 usually ignites an igniter material 42 that burns rapidly and exothermically, in turn, igniting a gas generant material 50.

The gas generant 50 can be in the form of a solid grain, a pellet, a tablet, or the like. “Slag” or “clinker” is another name for solid combustion products formed during combustion of the gas generant material. The composition of slag is mainly metals and metal oxides. Ideally, the slag will maintain the original shape of the gas generant (e.g., grain, pellet, or tablet) and be large and easily filtered. This is particularly important when the inflator design includes a reduced mass filtration system for the purpose of reducing the inflator size and weight such as can be used with cool burning gas generant formulations. As shown in FIG. 1, an exemplary conventional filter system 52 is provided between gas generant 50 and airbag 36. The quality and toxicity of the components of the gas produced by the gas generant 50, also referred to as effluent, are important because occupants of the vehicle are potentially exposed to these compounds. It is desirable to minimize the concentration of potentially harmful compounds in the effluent.

Various different gas generant compositions (e.g., 50) are used in vehicular occupant inflatable restraint systems. Gas generant material selection involves various factors, including meeting current industry performance specifications, guidelines and standards, generating safe gases or effluents, handling safety of the gas generant materials, durational stability of the materials, and cost-effectiveness in manufacture, among other considerations. It is preferred that the gas generant compositions are safe during handling, storage, and disposal, and preferably are azide-free.

In various aspects, the gas generant typically includes at least one fuel component and at least one oxidizer component, and may include other minor ingredients, that once ignited combust rapidly to form gaseous reaction products (e.g., CO₂, H₂O, and N₂). One or more fuel compounds undergo rapid combustion to form heat and gaseous products; e.g., the gas generant burns to create heated inflation gas for an inflatable restraint device or to actuate a piston. The gas-generating composition also includes one or more oxidizing components, where the oxidizing component reacts with the fuel component in order to generate the gas product.

Improved gas generator performance in an inflatable restraint system may be achieved in a variety of ways, many of which ultimately depend on the gas generant formulation to provide the desired properties. Ideally, a gas generant provides sufficient gas mass flow in a desired time interval to achieve the required work impulse for an inflating device (e.g., airbag) within the inflatable restraint system. Although a temperature of gas generated by the gas generant influences the amount of work gases can do, high gas temperatures may be undesirable because burns and related thermal damage can result. In addition, high gas temperatures can also potentially lead to an excessive reliance or sensitivity of the gas to heat transfer and excessively rapid deflation profiles, which can likewise be undesirable. For example, a cool burning gas generant having combustion flame temperatures of less than approximately 1,900K (1,627° C.) has been shown to enable inflator devices with reduced filtration, which operate in a manner that provides adequate restraint and protection, without the risk of burns or injury to an automobile occupant in the event of a crash. Thus, minimizing flame temperature is advantageous. In certain aspects of the present technology, a high flame temperature may be considered anything in excess of about 1,900K (1,627° C.) at combustion.

In order to mitigate the effects of high flame temperatures, in conventional inflatable restraint system gas generators, a significant portion of mass of an inflator is often relegated to heat sink in combination with filtration. This impacts the efficiency of the system and, most significantly, the weight of the inflator. Consequently, in certain aspects, it is desirable to provide a gas generant formulation for an inflatable restraint system that can achieve a high gas output at a high mass flow rate at relatively low flame temperatures. Furthermore, it would be desirable to employ a gas generant formulation that has enhanced slag forming abilities, so that attendant filter components can be reduced within the inflator component to further improve efficiency. Other important variables in inflator gas generant design include improving gas generant performance with respect to gas yield, relative quickness (as determined by observed burning rate), and cost.

Advanced inflator design concepts incorporate reduced filter and heat sink mass, as well as reduced containment wall thickness coupled with fiberglass/resin reinforcement to achieve significant weight reduction in the inflator. Use of cool burning gas generant formulations reduces heat sink requirements. Additionally, because filter mass is reduced, it is desirable to have a cool burning gas generant that slags very well. By “slagging” it is meant that certain solid combustion products generated during burning of the gas generant form a large integral solid mass that is retained inside the combustion chamber during combustion, rather than passing through the filter into the airbag. Traditional slagging agents have been used to achieve this effect. A slagging agent is a compound or material, usually inert to combustion, that melts at combustion temperatures and agglomerates or collects all of the solid combustion products together. Examples of conventional slagging agents are silicon dioxide, aluminum oxide, glass and other metal oxides that melt at or near the combustion flame temperature.

In various aspects, the present disclosure provides a relatively cool burning gas generant composition that comprises a fuel and an oxidizer. In certain embodiments, the gas generant composition comprises a fuel and an oxidizer comprising copper. In further embodiments, the gas generant comprises a fuel and an oxidizer comprising basic copper nitrate. In certain aspects, the gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.) and in certain other aspects, optionally less than or equal to about 1,700K (1,427° C.). In accordance with various aspects of the present teachings, a large particle size endothermic slag-forming component is introduced to the gas generant composition to significantly enhance formation of slag when such a gas generant component is combusted. The endothermic slag-forming component particles preferably have an average particle size diameter of greater than or equal to about 150 μm. In certain aspects, the endothermic slag-forming component has a decomposition temperature in a range of greater than or equal to about 180° C. to less than or equal to about 450° C., meaning that the compound decomposes endothermically within this temperature range, for example, by releasing water or carbon dioxide.

In certain preferred variations, the endothermic slag-forming component comprises a large particle size aluminum hydroxide (Al(OH)₃). However, in alternative variations, the following compounds may be employed as endothermic slag-forming components in gas generant compositions comprising copper: hydromagnesite (Mg₅(CO₃)₄(OH)₂.4H₂O), Dawsonite (NaAl(OH)₂CO₃), magnesium hydroxide (Mg(OH)₂), magnesium carbonate subhydrate (MgOCO₂.H₂O_((0.3))), Bohemite (AlO(OH)), calcium hydroxide (Ca(OH)₂), and combinations thereof. Each of these compounds decomposes endothermically within the desired temperature range of greater than or equal to about 180° C. to less than or equal to about 450° C., as set forth in Table 1 below.

TABLE 1 Decomposition Compound Chemical Formula Temperature ° C. Aluminum Hydroxide Al(OH)₃ 180-200 Hydromagnesite Mg₅(CO₃)₄(OH)₂•4H₂0 220-240 Dawsonite NaAl(OH)₂CO₃ 240-260 Magnesium Hydroxide Mg(OH)₂ 300-320 Magnesium Carbonate MgOCO₂•H₂O_((0.3)) 340-350 Subhydrate Bohemite AlO(OH) 340-350 Calcium Hydroxide Ca(OH)₂ 430-450

The endothermic slag-forming component has specific particle size requirements to provide certain benefits associated with the inventive technology. In certain embodiments, the endothermic slag-forming component comprises a large particle size aluminum hydroxide (Al(OH)₃). The inventive technology contemplates use of aluminum hydroxide having very specific particle size properties, which greatly improves slag formation while also cooling a copper-containing gas generant flame temperature (e.g., a maximum combustion flame temperature lowered to about 1,350K (1,077° C.)-1,450K (1,177° C.).

In certain variations, endothermic slag-forming component particles (e.g., aluminum hydroxide particles) have a large particle size. By “large particle size,” it is meant that an average particle size diameter of the endothermic slag-forming component particles (e.g., aluminum hydroxide particles) is greater than or equal to 150 micrometers (μm), optionally greater than or equal to about 175 μm, optionally greater than or equal to about 200 μm, optionally greater than or equal to about 225 μm, optionally greater than or equal to about 250 μm, optionally greater than or equal to about 275 μm, and in certain variations greater than or equal to about 300 μm. The particle size distribution for the endothermic slag-forming component particles may have a 10% value of greater than or equal to about 100 μm (micrometers); optionally greater than or equal to about 115 μm. In certain variations, the particle size distribution has an average (50%) particle size of greater than or equal to about 150 μm, while also having a 10% value of greater than or equal to about 100 μm. Furthermore, particle size distributions of endothermic slag-forming component particles with 90% values of 200 to 300 μm also provide desired advantages associated with certain aspects of the present teachings. One suitable example of a large particle size aluminum hydroxide has a particle size distribution 10% value of about 115 μm, a 50% value of about 158 μm (thus an average particle size diameter of 158 μm), and a 90% value of about 288 μm. An example of such an acceptable particle size for an aluminum hydroxide that fulfills the requirements for use in accordance with the present technology is shown in FIG. 2, which has an average particle size diameter as described just above. Thus, relatively large particles provide the desirable slagging ability to the gas generant compositions comprising copper.

In accordance with various aspects of the present disclosure, gas generants are provided that have desirable compositions that result in superior performance characteristics in an inflatable restraint device, while reducing overall cost of gas generant and inflator assembly production. Thus, in accordance with various aspects of the present teachings, an improved cool burning gas generant composition is provided that has a maximum combustion temperature (T_(c)) (also expressed as maximum combustion flame temperature) of less than or equal to about 1,900K (1,627° C.). In certain variations, the maximum combustion temperature is less than or equal to about 1,800K (1,527° C.), optionally less than or equal to about 1,700K (1,427° C.), optionally less than or equal to about 1,600K (1,327° C.) and in certain variations, less than or equal to about 1,500K (1,227° C.). In various embodiments, it is preferred that the flame temperature during combustion for a cool burning gas generant is greater than or equal to about 1,300K (1,027° C.) to less than or equal to about 1,700K (1,427° C.).

Additionally, in various aspects, the gas generant may have a high mass density in various embodiments. For example, in certain embodiments, the gas generant has a theoretical mass density of greater than or equal to about 2 g/cm³, optionally greater than or equal to about 2.25 g/cm³, optionally greater than or equal to about 2.5 g/cm³, and in certain variations, optionally greater than or equal to about 2.75 g/cm³.

Further, in accordance with the present disclosure, the gravimetric gas yield of the gas generant is relatively high. For example, in certain embodiments, the gravimetric gas yield is greater than or equal to about 1.8 moles/100 grams of gas generant. In other embodiments, the gravimetric gas yield is greater than or equal to about 1.9 moles/100 g of gas generant, optionally greater than or equal to about 2.0 moles/100 g of gas generant, optionally greater than or equal to about 2.1 moles/100 g of gas generant, optionally greater than or equal to about 2.2 moles/100 g of gas generant, optionally greater than or equal to about 2.3 moles/100 g of gas generant, optionally greater than or equal to about 2.4 moles/100 g of gas generant, optionally greater than or equal to about 2.5 moles/100 g of gas generant, and in certain variations, optionally greater than or equal to about 2.6 moles/100 g of gas generant. The product of gravimetric gas yield and density is a volumetric gas yield.

In other aspects, the volumetric gas yield of a gas generant according to certain variations of the present disclosure is optionally greater than or equal to about 5.0 moles/100 cm³ of gas generant. In other embodiments, the volumetric gas yield is greater than or equal to about 5.1 moles/100 cm³ of gas generant, optionally greater than or equal to about 5.2 moles/100 cm³ of gas generant, optionally greater than or equal to about 5.3 moles/100 cm³ of gas generant, optionally greater than or equal to about 5.4 moles/100 cm³ of gas generant, optionally greater than or equal to about 5.5 moles/100 cm³ of gas generant, and in certain variations, optionally greater than or equal to about 5.6 moles/100 cm³ of gas generant.

Thus, the present technology provides enhanced slag formation for cool burning gas generants. Thus, in certain aspects, the disclosure provides a gas generant composition comprising copper having good slag forming capabilities. For example, the gas generant composition may comprise at least one fuel, at least one oxidizer comprising copper, a large particle size endothermic slag-forming component, and optionally minor amounts of conventional gas generant additives. Materials are generally categorized as gas generant fuels due to their relatively low burn rates, and are often combined with one or more oxidizers in order to obtain desired burn rates and gas production. As appreciated by those of skill in the art, such a fuel component may be combined with additional components in the gas generant, such as co-fuels or oxidizers. Most fuels known in the art can be used with the present technology and are generally selected to impart certain desirable characteristics to the gas generant formulation, such as gas yield, burning rate, thermal stability, and low cost. These fuels can be organic compounds containing two or more of the elements: carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). The fuels can also include transition metal salts and transition metal nitrate complexes. In certain variations, preferred transition metals are copper and/or cobalt. In accordance with certain aspects of the present teachings, a fuel is selected for the inventive gas generant compositions so that when combusted with certain oxidizers comprising copper, such as basic copper nitrate, a resulting maximum combustion flame temperature (T_(c)) falls within a range of greater than or equal to about 1,400K (1,127° C.) to less than or equal to 1,900K (1,627° C.).

Examples of fuels useful for gas generants according to the present teachings are selected from the group consisting of guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof. Fuels may be used singly or in combination with other co-fuels to impart the desired combustion characteristics. A suitable gas generant composition optionally includes greater than or equal to about 25% to less than or equal to about 70% by weight; optionally greater than or equal to about 30% to less than or equal to about 55% of all fuel components in the total gas generant composition.

The gas generant formulations according to various aspects of the present teachings include an oxidizer comprising copper as a main oxidizer. A particularly suitable oxidizer for the gas generant compositions of the present disclosure is basic copper nitrate. Basic copper nitrate has a high oxygen-to-metal ratio and good slag forming capabilities upon burn. By way of example, a suitable gas generant composition optionally includes greater than or equal to about 25% to less than or equal to about 75% by weight of the oxidizer, such as basic copper nitrate; optionally greater than or equal to about 30% to less than or equal to about 60% by weight of the oxidizer, such as basic copper nitrate, in the total gas generant composition.

The gas generant may include combinations of oxidizers, such that the oxidizer comprising copper may be nominally considered to be a primary oxidizer, so that additional oxidizers are referred to as a secondary oxidizer, and the like. In certain variations, the gas generant composition may comprise an oxidizer comprising a perchlorate-containing compound (a compound including a perchlorate group (ClO₄ ⁻). In certain variations, the gas generant compositions may be substantially free of perchlorate-containing compounds. However, if such perchlorate-containing compounds are present in relatively small amounts, alkali, alkaline earth, and ammonium perchlorates are contemplated for use in the gas generant compositions. Particularly suitable perchlorate oxidizers include alkali metal perchlorates and ammonium perchlorates, such as ammonium perchlorate (NH₄ClO₄), sodium perchlorate (NaClO₄), potassium perchlorate (KClO₄), lithium perchlorate (LiClO₄), magnesium perchlorate (Mg(ClO₄)₂), and combinations thereof. If perchlorate oxidizers are present in the gas generant, it is preferably at less than about 3% by weight of the total gas generant composition. By way of example, a perchlorate containing oxidizer is present in certain embodiments at about 0.1% to about 3% by weight; and optionally about 0.5 to about 2% by weight of the gas generant.

As discussed above, in accordance with the present technology, the gas generant composition further comprises an endothermic slag-forming component having a large particle size. In certain variations, the endothermic slag-forming component is selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof. In various aspects, the endothermic slag-forming component may be present at greater than or equal to about 5% by weight to less than or equal to about 20% by weight of a total gas generant composition; optionally at greater than or equal to about 7% to less than or equal to about 18%; optionally at greater than or equal to about 8% to less than or equal to about 16%; and in certain variations, greater than or equal to about 10% to less than or equal to about 15% by weight of a total gas generant composition.

If desired, a gas generant composition may optionally include additional components known to those of skill in the art. Such additives typically function to improve the handling or other material characteristics of the slag which remains after combustion of the gas generant material; and improve ability to handle or process pyrotechnic raw materials. By way of non-limiting example, additional ingredients for the gas generant composition may be selected from the group consisting of: flow aids, pressing aids, metal oxides, and combinations thereof. If minor ingredients are included in the gas generant, they may be cumulatively present at less than or equal to about 4% by weight of the total gas generant composition. By way of example, such an additive may be selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof is present in a gas generant composition, in certain variations each respective additive is present at greater than or equal to 0% to less than or equal to about 3% by weight; optionally greater than or equal to about 0.1% to less than or equal to about 2% by weight, and in certain variations, optionally greater than or equal to about 0.5% to less than or equal to about 1% by weight of the gas generant, so that the total amount of additives is less than or equal to about 4%.

Press aids used during compression processing, include lubricants and/or release agents, such as graphite, calcium stearate, magnesium stearate, molybdenum disulfide, tungsten disulfide, graphitic boron nitride, may be optionally included in the gas generant compositions, by way of non-limiting example. Conventional flow aids may also be employed, such as high surface area fumed silica.

The gas generant compositions may optionally include a metal oxide that serves as a viscosity modifying compound or an additional slag forming agent (in addition to the endothermic slag-forming component described above). Suitable metal oxides may include silicon dioxide, cerium oxide, ferric oxide, titanium oxide, zirconium oxide, bismuth oxide, molybdenum oxide, lanthanum oxide and the like.

A gas generant composition according to certain aspects of the present disclosure comprises a fuel component, an oxidizer comprising basic copper nitrate, and an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.). The gas generant composition may further comprise a co-oxidizer, such as a perchlorate-based compound. In certain variations, a gas generant composition comprises greater than or equal to about 5% to less than or equal to about 70% by weight of the gas generant composition, an oxidizer comprising basic copper nitrate present at greater than or equal to about 25% to less than or equal to about 75% by weight of the gas generant composition, a co-oxidizer comprising a perchlorate-based compound present at greater than or equal to 0% to less than or equal to about 3% by weight of the gas generant composition, and an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm present at greater than or equal to about 5% to less than or equal to about 20% by weight of the gas generant composition. In certain variations, the gas generant composition may further comprise an additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof, wherein a cumulative amount of the additive(s) is greater than or equal to 0% to less than or equal to about 4% of the gas generant composition. The inventive gas generant formulations are cool burning and show a significant improvement in slagging, as will be discussed in greater detail below.

In other variations, a gas generant composition comprises a fuel selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof, present at greater than or equal to about 25% to less than or equal to about 70% by weight. The gas generant also comprises an oxidizer comprising basic copper nitrate present at greater than or equal to about 25% to less than or equal to about 75% by weight of the gas generant composition. In certain aspects, the gas generant composition may further comprise a co-oxidizer, such as a perchlorate-based compound present at greater than or equal to 0% to less than or equal to about 3%. Further, the gas generant includes an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof, which is present at greater than or equal to about 5% to less than or equal to about 20% by weight of the gas generant composition. In certain variations, the gas generant composition comprises an additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof, where a cumulative amount of the additive(s) is greater than or equal to 0% to less than or equal to about 4% of the gas generant composition. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.) and can achieve a resultant flame temperature of between about 1,350K (1,077° C.) to 1,450K (1,177° C.).

In certain other variations, a gas generant composition comprises a fuel comprising guanidine nitrate present at greater than or equal to about 25% to less than or equal to about 70% by weight. The gas generant also includes an oxidizer comprising basic copper nitrate at greater than or equal to about 25% to less than or equal to about 75% by weight of the gas generant composition. In certain variations, a co-oxidizer is optionally present, for example a co-oxidizer that comprises a perchlorate-based compound present at greater than or equal to 0% to less than or equal to about 3% by weight of the gas generant composition. Further, the gas generant includes an endothermic slag-forming component comprising aluminum hydroxide (Al(OH)₃) having an average particle size diameter of greater than or equal to about 150 μm present at greater than or equal to about 5% to less than or equal to about 20% by weight of the gas generant composition. In certain variations, such a gas generant composition optionally comprises an additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof, where a cumulative amount of the additive(s) is greater than or equal to 0% to less than or equal to about 4% of the gas generant composition. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.) and can achieve a resultant flame temperature of between about 1,350K (1,077° C.) to 1,450K (1,177° C.).

In yet other variations, a gas generant composition according to certain aspects of the present disclosure consists essentially of a fuel component, an oxidizer comprising basic copper nitrate, and an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.). In certain variations, a gas generant composition consists essentially of greater than or equal to about 25% of a fuel to less than or equal to about 70% by weight of the gas generant composition, an oxidizer comprising basic copper nitrate present at greater than or equal to about 25% to less than or equal to about 75% by weight of the gas generant composition, a co-oxidizer comprising a perchlorate-based compound present at greater than or equal to 0% to less than or equal to about 3% by weight of the gas generant composition, and an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm present at greater than or equal to about 5% to less than or equal to about 20% by weight of the gas generant composition and an optional additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof, wherein a cumulative amount of the additive(s) is greater than or equal to 0% to less than or equal to about 4% of the gas generant composition.

In other variations, a gas generant composition consists essentially of a fuel selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof; an oxidizer comprising basic copper nitrate; a co-oxidizer comprising a perchlorate-based compound present at greater than or equal to 0% to less than or equal to about 3% by weight of the gas generant composition; an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof; and an optional additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.) and can achieve a resultant flame temperature of between about 1,350K (1,077° C.) to 1,450K (1,177° C.).

In yet other variations, a gas generant composition consists essentially of a fuel selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof, present at greater than or equal to about 25% to less than or equal to about 70% by weight; an oxidizer comprising basic copper nitrate present at greater than or equal to about 25% to less than or equal to about 75% by weight of the gas generant composition; a co-oxidizer comprising a perchlorate-based compound present at greater than or equal to 0% to less than or equal to about 3% by weight of the gas generant composition; an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof, which is present at greater than or equal to about 5% to less than or equal to about 20% by weight of the gas generant composition; and an optional additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof, where a cumulative amount of the additive(s) is greater than or equal to 0% to less than or equal to about 4% of the gas generant composition. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.) and can achieve a resultant flame temperature of between about 1,350K (1,077° C.) to 1,450K (1,177° C.).

In certain other variations, a gas generant composition consists essentially of a fuel comprising guanidine nitrate, an oxidizer comprising basic copper nitrate, a co-oxidizer comprising a perchlorate-based compound, an endothermic slag-forming component comprising aluminum hydroxide (Al(OH)₃) having an average particle size diameter of greater than or equal to about 150 μm, and an optional additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.).

In other embodiments, a gas generant composition consists essentially of a fuel comprising guanidine nitrate, an oxidizer comprising basic copper nitrate, an endothermic slag-forming component comprising aluminum hydroxide (Al(OH)₃) having an average particle size diameter of greater than or equal to about 150 μm, and an optional additive selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof. In certain variations, the fuel comprising guanidine nitrate is present at greater than or equal to about 25% to less than or equal to about 70% by weight. The oxidizer comprising basic copper nitrate can be present at greater than or equal to about 25% to less than or equal to about 75% by weight of the gas generant composition. Further, the aluminum hydroxide is present at greater than or equal to about 5% to less than or equal to about 20% by weight of the gas generant composition. The additive or additives may be present in a cumulative total amount of greater than or equal to 0% to less than or equal to about 4% of the gas generant composition. Such a gas generant composition preferably has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.).

Example 1

Experiments are performed to determine the effect of aluminum hydroxide particle size on slag formation in a representative gas generant formulation. Comparative Example 1 has a conventional smaller size of aluminum hydroxide particle, while Example 2 is prepared in accordance with certain aspects of the present teachings. The ingredients for the gas generant and their properties for both Comparative Example 1 and Example 2 are given in Table 2.

TABLE 2 Comparative Ingredient Example 1 Example 2 % basic copper nitrate 38.68 38.68 % guanidine nitrate 17.27 17.27 % copper bis guanylurea dinitrate 28.84 28.84 % glass fibers 0.88 0.88 % aluminum hydroxide 14.32 14.32 10% Particle Size Distribution (PSD) 54 μm 115 μm Aluminum Hydroxide 50% PSD Aluminum Hydroxide 87 μm 158 μm 90% PSD Aluminum Hydroxide 152 μm  228 μm Flame Temperature K 1,400 1,400

The respective formulations are prepared and pressed into 0.5″ diameter by 0.43″ cylinders at 12,000 lbs force. These samples are prepared by spray drying a formulation containing guanidine nitrate, basic copper nitrate, copper bis guanylurea dinitrate, and glass fibers. The spray dried formulation is then dry blended with the different particle size aluminum hydroxide and pressed into the 0.5×0.43″ diameter cylinder. Cylinders are then burned in a 1 liter enclosed bomb under 3,000 psi nitrogen. Slag from Comparative Example 1, although in the shape of the original cylinder, had very low density and fell apart to the touch. Slag from Example 2 maintains the shape of the original cylinder, has good density, and does not fall apart when handling. Macroscopic and microscope pictures of slag from Comparative Example 1 and Example 2 are shown in FIGS. 3-4 (Comparative Example 1) and 5-6 (Example 2), respectively. Magnification is 50× in the microscopic pictures in FIGS. 4 and 6.

The combustion slag in FIG. 4 shows spheres of molten copper and spheres of aluminum oxide loosely associated with each other, which results in very weak slag that falls apart and can breach the filter and enter the airbag during deployment. The combustion slag in FIG. 6 shows large spheres of aluminum oxide coated and surrounded by a molten copper matrix. This results in slag with greater structural strength that resists coming apart and breaching the filter during combustion. While not limiting the present disclosure to any particular theory, it is believed that a larger particle size aluminum hydroxide stays cooler longer during combustion, for example, due to reduced surface area and slower heat transfer, as compared to smaller particles of aluminum hydroxide. The cooler surfaces thus can provide a site for molten copper to condense on as it is formed resulting in an improved slagging product.

Example 2

Gas generants of Comparative Example 1 and Example 2 described in the context of Example 1 are also pressed into 0.25″ diameter×0.060″ tablets, loaded into a driver side automotive airbag inflator, and deployed into a 60 liter tank. After deployment, the tank is washed down and the wash water collected. The insoluble particulate is captured on a filter and weighed after drying. Any soluble particulate is precipitated by evaporation of the wash water and weighed. The total particulate escaping the combustion filter is determined by adding the weights of the soluble and insoluble particulate found in the tank. This value is called the “tank wash value.”

Tank wash values for gas generants from Comparative Example 1 and Example 2 are given in Table 3.

TABLE 3 Comparative Example 1 Example 2 Tank Wash (g) 2.5-3.9 0.5-0.9

As shown in Table 3, the amount of particulate escaping the filter is greatly reduced when using the inventive gas generant from Example 2 (having a large particle size aluminum hydroxide), as compared to gas generant from Comparative Example 1 (having a small particle size aluminum hydroxide). For example, a minimum reduction of tank wash value (and thus enhancement of slag formation) is 64%, while a maximum reduction of tank wash value is 87%. An average reduction in tank wash value is 78%. Thus, by introducing large particle size aluminum hydroxide in accordance with certain aspects of the present disclosure, a significant enhancement in slag formation occurs for gas generant compositions.

The inflator combustion chambers from these tests are machined open and the combustion slag is visually examined. Pictures of the post-fire combustion slags from Comparative Example 1 and Example 2 are shown in FIGS. 7 and 8. As the pictures show, the slag in FIG. 7 from gas generant in Comparative Example 1 is very weak, most of it ending up as a loose powder in the combustion chamber. The slag in FIG. 8 from an inventive gas generant in Example 2 is quite intact, maintaining the shape of the original tablets with very little loose powder present.

Thus, in certain aspects, the present disclosure provides a method of enhancing slag formation for a gas generant composition. The method comprises introducing an endothermic slag-forming component having an average particle diameter size of greater than or equal to about 150 μm to a gas generant composition that comprises copper. In certain embodiments, the gas generant comprises a fuel and an oxidizer comprising copper. In further embodiments, the gas generant comprises a fuel and an oxidizer comprising basic copper nitrate. Any of the gas generant compositions described previously above are contemplated. Similarly, any of the endothermic slag-forming components described previously are contemplated for use in these methods. The introducing of the endothermic slag-forming component enhances slag formation during combustion of the gas generant composition by at least 50%, as measured by reduced tank wash values. In certain variations, such methods desirably enhance slag formation by at least 55%, optionally by at least 60%, optionally by at least 63%, optionally by at least 64%, optionally by at least 65%, optionally by at least 70%, optionally by at least 75%, optionally by at least 78%, optionally by at least 80%, optionally by at least 85%, and in certain variations, optionally by at least 87%.

In certain aspects, the gas generant composition to which the endothermic slag-forming component is added has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.), where the fuel is selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof. The endothermic slag-forming component may be selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof. In certain variations, the maximum flame temperature at combustion (T_(c)) of the gas generant is greater than or equal to about 1,350K (1,077° C.) to less than or equal to about 1,450K (1,177° C.).

In certain preferred variations, the endothermic slag-forming component introduced to the gas generant, which enhances slag formation, comprises aluminum hydroxide and is present at greater than or equal to about 5% by weight to less than or equal to about 20% by weight of a total gas generant composition. Thus, introducing a large particle size aluminum hydroxide, for example, with an average particle diameter size of greater than or equal to about 150 μm, into a gas generant provides a desirably cool burning gas generant that has superior, enhanced slag formation.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A gas generant composition comprising: a fuel; an oxidizer comprising basic copper nitrate; and an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm, wherein the gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.).
 2. The gas generant composition of claim 1, wherein the endothermic slag-forming component has a decomposition temperature in a range of greater than or equal to about 180° C. to less than or equal to about 450° C.
 3. The gas generant composition of claim 1, wherein the endothermic slag-forming component is present at greater than or equal to about 5% by weight to less than or equal to about 20% by weight of the total gas generant composition.
 4. The gas generant composition of claim 1, wherein the endothermic slag-forming component is selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof.
 5. The gas generant composition of claim 1, wherein the fuel is selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof.
 6. The gas generant composition of claim 1, wherein the oxidizer comprising basic copper nitrate is present at greater than or equal to about 30% to less than or equal to about 70% by weight of the gas generant composition.
 7. The gas generant composition of claim 1, wherein the endothermic slag-forming component has an average particle size diameter of greater than or equal to about 200 μm.
 8. The gas generant composition of claim 1, wherein the fuel is present at greater than or equal to about 25% to less than or equal to about 70% by weight of the total gas generant composition; the oxidizer is present at greater than or equal to about 25% to less than or equal to about 75% by weight of the total gas generant composition; the endothermic slag-forming component is present at greater than or equal to about 5% to less than or equal to about 20% by weight of the total gas generant composition; and greater than or equal to 0% to less than or equal to about 4% of one or more gas generant additives selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof.
 9. The gas generant composition of claim 8, further comprising a co-oxidizer comprising a perchlorate-based compound present at greater than 0% to less than or equal to about 3% by weight of the total gas generant composition.
 10. A gas generant composition comprising: a fuel; at least one oxidizer comprising basic copper nitrate; and an endothermic slag-forming component comprising aluminum hydroxide having an average particle size diameter of greater than or equal to about 150 μm, wherein the gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.).
 11. The gas generant composition of claim 10, wherein the maximum flame temperature at combustion (T_(c)) is greater than or equal to about 1,350K (1,077° C.) to less than or equal to about 1,450K (1,177° C.).
 12. The gas generant composition of claim 10, wherein the endothermic slag-forming component comprising aluminum hydroxide is present at greater than or equal to about 5% by weight to less than or equal to about 20% by weight of the total gas generant composition.
 13. The gas generant composition of claim 10, wherein the fuel is selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof.
 14. The gas generant composition of claim 10, wherein the endothermic slag-forming component comprising aluminum hydroxide has an average particle size diameter of greater than or equal to about 200 μm.
 15. The gas generant composition of claim 10, wherein the fuel is present at greater than or equal to about 25% to less than or equal to about 70% by weight of the total gas generant composition; the oxidizer is present at greater than or equal to about 25% to less than or equal to about 75% by weight of the total gas generant composition; the endothermic slag-forming component is present at greater than or equal to about 5% to less than or equal to about 20% by weight of the total gas generant composition; and greater than or equal to 0% to less than or equal to about 4% of one or more gas generant additives selected from the group consisting of: flow aids, press aids, metal oxides, and combinations thereof.
 16. The gas generant composition of claim 15, further comprising a co-oxidizer comprising a perchlorate-based compound present at greater than 0% to less than or equal to about 3% by weight of the total gas generant composition.
 17. A method of enhancing slag formation for a gas generant composition, the method comprising: introducing an endothermic slag-forming component having an average particle size diameter of greater than or equal to about 150 μm to a gas generant composition comprising a fuel and an oxidizer comprising basic copper nitrate, wherein the introducing of the endothermic slag-forming component enhances slag formation during combustion of the gas generant composition by at least 50%.
 18. The method of claim 17, wherein the gas generant composition has a maximum flame temperature at combustion (T_(c)) of less than or equal to about 1,900K (1,627° C.), the fuel is selected from the group consisting of: guanidine nitrate, copper bis guanylurea dinitrate, hexamine cobalt (III) nitrate, copper diammine bitetrazole, and combinations thereof, and the endothermic slag-forming component is selected from the group consisting of: aluminum hydroxide, hydromagnesite, Dawsonite, magnesium hydroxide, magnesium carbonate subhydrate, Bohemite, calcium hydroxide, and combinations thereof.
 19. The method of claim 17, wherein the endothermic slag-forming component enhancing slag formation comprises aluminum hydroxide and is present at greater than or equal to about 5% by weight to less than or equal to about 20% by weight of the total gas generant composition.
 20. The method of claim 17, wherein the introducing of the endothermic slag-forming component enhances slag formation during combustion of the gas generant composition by at least 60%. 